Project Summary/Abstract Cardiovascular disease (CVD) is the leading cause of death among adults with diabetes mellitus (DM) and epidemiologic data indicate a significant relationship between postprandial hyperglycemia and CVD events. Chronic hyperglycemia contributes to endothelial dysfunction and consequently to DM-associated micro- and macrovascular complications. In persons with and without DM, CVD is associated with functional alterations in the vascular endothelium, including defective endothelial-directed, nitric-oxide-dependent vasoregulation. Microvascular perfusion (MP) plays a key role in nutrient, hormone, and gas delivery to and from tissues. Real- time measurement of MP provides the best estimate of dynamic changes in endothelial surface area available for nutrient, hormone, and oxygen exchange. Surprisingly, despite the known linkage between postprandial hyperglycemia and CVD events, the effects of acute hyperglycemia (AH) on MP in humans have not been thoroughly investigated. Using contrast-enhanced ultrasound (CEU), we compared forearm muscle microvascular insulin responses in type 1 DM (T1DM) patients (without known microvascular complications) with responses in weight- and age-matched controls. The distinguishing clinical feature between groups was hyperglycemia in the T1DM subjects. Insulin increased microvascular blood volume (a marker for endothelial surface exposure and MP) measured by CEU in control but not T1DM subjects. We have previously demonstrated that physiologic hyperinsulinemia increases MP in both skeletal and cardiac muscle in healthy humans when subjects remained euglycemic. Hyperinsulinemia can lessen AH-induced macrovascular endothelial dysfunction in obese humans, but whether this extends to the microvasculature is unknown. The research proposed herein addresses the hypotheses that (a) AH rapidly (within 3.5 hours) impairs MP in both cardiac and skeletal muscle; and (b) insulin mitigates AH's adverse effect on cardiac and skeletal muscle MP in healthy insulin-sensitive subjects. In the proposed studies, we will utilize CEU to (1) directly assess the effects of AH on skeletal and cardiac muscle MP and (2) test whether physiologic hyperinsulinemia will mitigate AH's adverse effect on cardiac and skeletal muscle MP in healthy insulin-sensitive subjects. The proposed studies will fill a gap in current knowledge and provide the first comprehensive investigation of the effects of AH on skeletal and cardiac muscle microvascular function in healthy individuals. Our functional approach to evaluating MP may provide a testing paradigm for future interventions that could mitigate the adverse effects of AH on important microvascular beds.